This is the Titan's Curse.
Percy, Annabeth, and Thalia go to Westover Hall after Grover finds two demigod siblings named Nico and Bianca. They are attacked by a manticore named Dr. Thorn, but are saved by Artemis and her hunters, including one named Zoe Nightshade;Annabeth is captured by Dr. Thorn.
Artemis went to hunt down an unknown monster but got kidnapped by the 'general'. Three hunters (including Zoe Nightshade and Bianca de Angelo) Thalia, and Grover went to find the goddess following a prophecy. 'Five shall go wests to the goddess in chains, One shall be lost in the land without rain, The bane of Olympus shows the trail, Campers and Hunters combined prevail, The Titan's curse must one withstand, And one shall perish by a parent's hand'. A hunter that was going on the mission, got poisoned with centuar blood forcing her to stay behind.The group had to leave with out her. Percy, unable to stay back at camp while Annabeth was in danger, decided to follow the group. Percy calls on Blackjack, a Pegasus he liberated in The Sea of Monsters, to help him catch up. When they stop to rest briefly on top of the C Dionysus snares Percy and Blackjack in grape vines. But the god decided to let him go after telling him a story about a betrayed girl who the god marries. Percy escaped and sees Dr. Thorn, who he follows into the National Air and Space Museum,with Annabeth's invisibility cap. He sees Dr. Thorn with "the General" using dinosaur teeth that grow into skeleton warriors. Percy races to tell his friends about these warriors at the National Air and Space Museum, but they are attacked by the Nemean Lion, which they subdue. The group reluctantly agrees to let Percy come on the quest. They take several subway trains to escape the skeleton warriors. Apollo helps them and takes them to a little ski town against Zeus's orders. There they get attacked by the skeleton warriors. Grover gets a blessiing from Pan , the god of the wild, it was the Erymanthian Boar. After they managed to subdue it for a short time, they jump on it and it takes them to the "junkyard of the gods" in Gila Claw, Arizona. When rested there, Percy and his friends find out that Bianca and Nico were trapped in a hotel called 'Lotus Casino'. It was made so that nobody who ever entered wanted to come out. The Di Angelos were kept in there for seventy years until a lawyer came and told them that they had to leave. After some time Percy meets Ares, who secretly loves Aphrodite, and takes Percy to speak with Aphrodite, who insists that Percy is deeply in love with Annabeth. She warns him to not pick up anything in the junkyard. When they go through the 'junkyard of the gods' Bianca tries to steal a figurine from the mythomagic game for Nico, because that is the only figurine he never got for his game. Talos , the guardian, woke and started attacking them. Percy comes up with a plan and Bianca decided to be the one to go inside the metal giant and destroy it. She suceeded but was killed as well. Percy remebered the prophecy 'One shall be lost in the land without rain'.
When Percy and his friend are attacked by skeletal warriors at Hoover, Percy is saved by a mortal with the ability to see through the mist, Rachel Elizabeth Dare. Rachel confuses the skeletons and allows Percy and his friends to escape.
At the advice of Apollo, Percy consults Nereus about what the monster is that could destroy Olympus. Nereus says that the monster is Bessie, the Ophiotaurus that Percy saved. Dr. Thorn and his henchmen then ambush the demigods. Dr. Thorn tries to coax Thalia into killing and burning the Ophiotaurus, which would give her the power to kill the gods. Percy, Zoe, and Grover pull her away. They then agree to send the Ophiotaurus to Olympus with Grover, and give Poseidon the skin of the Nemean Lion as an offering. They go to seek the help of Annabeth's father. Going to the Garden of Hesperides, the dragon Ladon poisons Zoe as she tries to help Percy and Thalia cross. They continue up to Mount Othrys, where Artemis is holding up the sky as part of the Titan's curse. It is revealed that the 'general' was Atlas, Zoe's dad. Percy takes the burden as he is prophesized to, releasing Artemis and she tricks Atlas into taking the burden back. Annabeth is rescued and Zoe dies while saving Artemis and Percy and from her poisoned wound. While she's dying she confesses to Percy that she had betrayed her family to save Hercules and that Riptide was her immortal power. She then admitted that Percy was different from other men who betrayed women and said that she was honoured that he carried her sword. Artemis transforms her into a constellation after she dies.
The gods debate whether or not to kill Percy and the Ophiotaurus, but voted for their survival. Bessie will be kept in Olympus. When the group goes back to Camp Half-Blood, Percy tells Nico what happened to his sister, and the boy blames Percy. Suddenly they get ambushed by the skeleton warriors, Percy tried to fight them of telling Nico to run. But Nico sent them to the Underworld by shouting 'go away'. Percy realizes and tells Annabeth and Grover that Nico is a son of Hades; they vow to keep it a secret.
Artemis went to hunt down an unknown monster but got kidnapped by the 'general'. Three hunters (including Zoe Nightshade and Bianca de Angelo) Thalia, and Grover went to find the goddess following a prophecy. 'Five shall go wests to the goddess in chains, One shall be lost in the land without rain, The bane of Olympus shows the trail, Campers and Hunters combined prevail, The Titan's curse must one withstand, And one shall perish by a parent's hand'. A hunter that was going on the mission, got poisoned with centuar blood forcing her to stay behind.The group had to leave with out her. Percy, unable to stay back at camp while Annabeth was in danger, decided to follow the group. Percy calls on Blackjack, a Pegasus he liberated in The Sea of Monsters, to help him catch up. When they stop to rest briefly on top of the C Dionysus snares Percy and Blackjack in grape vines. But the god decided to let him go after telling him a story about a betrayed girl who the god marries. Percy escaped and sees Dr. Thorn, who he follows into the National Air and Space Museum,with Annabeth's invisibility cap. He sees Dr. Thorn with "the General" using dinosaur teeth that grow into skeleton warriors. Percy races to tell his friends about these warriors at the National Air and Space Museum, but they are attacked by the Nemean Lion, which they subdue. The group reluctantly agrees to let Percy come on the quest. They take several subway trains to escape the skeleton warriors. Apollo helps them and takes them to a little ski town against Zeus's orders. There they get attacked by the skeleton warriors. Grover gets a blessiing from Pan , the god of the wild, it was the Erymanthian Boar. After they managed to subdue it for a short time, they jump on it and it takes them to the "junkyard of the gods" in Gila Claw, Arizona. When rested there, Percy and his friends find out that Bianca and Nico were trapped in a hotel called 'Lotus Casino'. It was made so that nobody who ever entered wanted to come out. The Di Angelos were kept in there for seventy years until a lawyer came and told them that they had to leave. After some time Percy meets Ares, who secretly loves Aphrodite, and takes Percy to speak with Aphrodite, who insists that Percy is deeply in love with Annabeth. She warns him to not pick up anything in the junkyard. When they go through the 'junkyard of the gods' Bianca tries to steal a figurine from the mythomagic game for Nico, because that is the only figurine he never got for his game. Talos , the guardian, woke and started attacking them. Percy comes up with a plan and Bianca decided to be the one to go inside the metal giant and destroy it. She suceeded but was killed as well. Percy remebered the prophecy 'One shall be lost in the land without rain'.
When Percy and his friend are attacked by skeletal warriors at Hoover, Percy is saved by a mortal with the ability to see through the mist, Rachel Elizabeth Dare. Rachel confuses the skeletons and allows Percy and his friends to escape.
At the advice of Apollo, Percy consults Nereus about what the monster is that could destroy Olympus. Nereus says that the monster is Bessie, the Ophiotaurus that Percy saved. Dr. Thorn and his henchmen then ambush the demigods. Dr. Thorn tries to coax Thalia into killing and burning the Ophiotaurus, which would give her the power to kill the gods. Percy, Zoe, and Grover pull her away. They then agree to send the Ophiotaurus to Olympus with Grover, and give Poseidon the skin of the Nemean Lion as an offering. They go to seek the help of Annabeth's father. Going to the Garden of Hesperides, the dragon Ladon poisons Zoe as she tries to help Percy and Thalia cross. They continue up to Mount Othrys, where Artemis is holding up the sky as part of the Titan's curse. It is revealed that the 'general' was Atlas, Zoe's dad. Percy takes the burden as he is prophesized to, releasing Artemis and she tricks Atlas into taking the burden back. Annabeth is rescued and Zoe dies while saving Artemis and Percy and from her poisoned wound. While she's dying she confesses to Percy that she had betrayed her family to save Hercules and that Riptide was her immortal power. She then admitted that Percy was different from other men who betrayed women and said that she was honoured that he carried her sword. Artemis transforms her into a constellation after she dies.
The gods debate whether or not to kill Percy and the Ophiotaurus, but voted for their survival. Bessie will be kept in Olympus. When the group goes back to Camp Half-Blood, Percy tells Nico what happened to his sister, and the boy blames Percy. Suddenly they get ambushed by the skeleton warriors, Percy tried to fight them of telling Nico to run. But Nico sent them to the Underworld by shouting 'go away'. Percy realizes and tells Annabeth and Grover that Nico is a son of Hades; they vow to keep it a secret.